The Silicon Carbide Manufacturing Process

Silicon carbide is one of the two hardest materials on Earth. However, its precision requires precision machining operations and the quality is closely tied to its crystal orientation.

Before SiC is used in different applications, it must first be properly classified, milled and chemically treated to achieve desired properties. After these preliminary processes have taken place, SiC should then be chemically modified in order to meet customer specifications.

Raw Materials

Silicon carbide, a crystalline material composed of both silicon and carbon atoms, is one of the hardest materials known. With second only diamond and cubic boron nitride for hardness, silicon carbide makes an excellent material for abrasive and refractory applications, superior strength and chemical resistance properties as well as meeting electrical vehicle requirements in terms of driving range extension and overall vehicle efficiency.

Silicon carbide differs from many manufactured minerals in that it does not occur naturally in large quantities; rather it is produced through the carbothermic reduction process in a special smelting furnace at high temperatures.

Producing synthetic silicon carbide requires an intensive and energy-intensive process. Much of the silicon consumed during production of synthetic silicon carbide is lost, making it an expensive raw material. Furthermore, handling this hazardous substance requires expert knowledge in its production.

Silicon carbide manufacturing process begins with raw materials like flake graphite, elemental silicon, boron carbide powder and clay, which is then mixed and formed into mud before being loaded into a graphite-silicon carbide crucible and placed under isostatic press – compressing the mud to form solid cylindrical ingots with concentric layers that decrease in SiC content with distance from its core; final products can either be black or green depending on raw material composition.

Once the ingot has cooled, it can be processed further to meet specific applications. Crude silicon carbide can then be crushed, classified, milled again if necessary and chemically treated to achieve the properties for either abrasive or refractory uses.

Silicon carbide manufacturing processes can be lengthy. Removing impurities is essential, with polymorphic inclusions often being responsible for lower product yield. Once these impurities have been removed, ground diamond abrasives of various sizes must be used to smooth surfaces and eliminate knife marks before polishing to achieve global planarization for CMP processing.

Chemical Reactions

Silicon Carbide (SiC) is an ultrahard ceramic material with a Mohs scale rating of 9 on the Mohs scale – higher than diamond and close to being the hardest synthetic material known. SiC is strong, wear-resistant and boasts excellent thermal conductivity ratings compared to other ceramics such as Zirconia or Alumina. Furthermore, SiC boasts great chemical corrosion resistance compared to these ceramics while being highly thermal shock resistant without being attacked by acids, alkalis or molten salts.

SiC is produced for use in various industrial sectors by mixing pure silica sand with carbon in the form of coke in an electrical resistance furnace, followed by passing electric current through it to activate chemical reactions which convert carbon to silicon and oxygen gases before withdrawing the produced silicon dioxide and methane gas and producing solid SiC compounds that can then be used in various applications.

Reaction-bonded silicon carbide (RBSC) is produced by mixing coarse SiC powder with powdered carbon and plasticizers in order to form the desired shape, burning off any plasticizer residue, then heating the pieces at high temperatures in order to expose them to liquid or vapour silicon, which reacts with carbon to form additional silicon carbide which bonds to existing amorphous SiC material and crystallises into an orderly structure.

Chemical vapor deposition, a popular process in semiconductor production, can be more cost-effective than using this technique to grow cubic SiC; however, both methods require significant amounts of energy and equipment for growth.

RBSC has many applications and is often found in furniture kilns due to its excellent thermal shock resistance. Furthermore, this abrasive ceramic is used in car brakes, clutches and bulletproof vests due to its superior mechanical strength. Furthermore, power semiconductors made of this ceramic form an integral part of electric vehicles because of its ability to withstand high voltage demands without increasing battery management system size or weight – another useful aspect.

Heat Treatment

Silicon carbide, also referred to as carborundum or synthetic moissanite (/krbrnm/), is an inorganic chemical compound composed of silicon and carbon. While natural forms exist as rare mineral formations like moissanite, mass production allows its powder form to be mass used as an abrasive and hard ceramic. Other applications for silicon carbide include bulletproof vests and car brakes that require high endurance levels.

SiC is produced primarily using silica and graphitized petroleum coke carbon as its raw materials, which is then reduced using carbothermal reduction technology in an Acheson furnace for green-colored production. Auxiliary raw materials like sawdust and salt may also be utilized but do not take part in chemical reactions essential to production of SiC.

Once green-colored SiC has been formed, it must be accurately sorted and processed for different applications. Machined, smelted or chemically treated processes may be utilized to modify its properties further and improve strength and durability. SiC is an extremely strong material which can withstand extreme temperatures; additionally it resists corrosion and thermal shock making it suitable for harsh environments such as aerospace, power electronics, automotive, chemical and petrochemical industries.

Steel’s exceptional strength, wear resistance and chemical inertness make it an exceptional abrasive and ceramic material. Furthermore, its excellent electrical conductivity allows it to serve as an efficient electrical conductor; heavy doping of silicon or phosphorus to produce metallic semiconductors is another possibility; other doping possibilities include doping with boron, gallium and aluminium.

Polishing SiC material is one of the most difficult steps in its manufacturing process, owing to its brittle nature. Cutting, grinding, and polishing the surface requires considerable precision without losing precious raw material or reducing usable part ratio. Traditional diamond-bonded multi-wire cutting systems can be slow, expensive, and produce vast waste products that detract from manufacturing efficiency.

BLOHM, MAGERLE and STUDER have recently introduced an advanced SiC polishing technology that can process both faces and ODs of an SiC boule with minimal material loss in just one step, significantly increasing efficiency, lowering production costs and producing usable chips per batch. Furthermore, its improved quality meets customer demands such as higher voltage that enables electric vehicle drivers to travel further on one charge.

Surface Treatment

Silicon Carbide (SiC) is an extremely hard refractory material, second only to diamond and cubic boron nitride in hardness. Additionally, its properties make it suitable for abrasive and ceramic applications due to its wear resistance, inertness against all acids/alkalies/bases and thermal resistance properties. These qualities make SiC ideal for both grinding applications as well as ceramic production processes such as Acheson process sintering at 2200 degrees Celsius to produce ingots that undergo further processing; this makes its preparation even simpler and ensures optimal performance during manufacture of SiC material production processes.

Mechanical polishing of an ingot at a specific angle results in mechanically creating a modified layer on its surface that has an impactful influence on bonding with epoxy adhesives. Etching caused by mechanical polishing produces this modification layer; using conventional chemical-mechanical polishing techniques it takes five thousand hours to eliminate this modification layer completely.

Studies were undertaken with the goal of strengthening the bond between silicon carbide and epoxy adhesive by employing various surface treatments, with scanning electron microscopy being used to characterise three samples – control, refired and KrF laser processed samples. The as-received sample had a dark glossy grey appearance; while refired samples displayed glassy surfaces. Finally, laser processed samples displayed different morphologies. X-ray photoelectron spectroscopy showed that both refiring and laser processing processes had led to surface oxidization of an ingot, with laser processed samples having greater concentrations of hydroxyl groups than controls. Refiring and laser processes were found to increase the polar component of surface energy, which may help improve wettability and thus bond strength. Tensile and shear testing revealed that laser processed and refired samples exhibited improved bond strengths compared to as received samples, due to an oxidised surface and higher polar component of surface energy. Furthermore, it was determined that using Toyo Tanso’s product PERMA KOTE significantly enhanced their oxidation resistance during processing.